1. Field of the Invention
The present invention relates to an acceleration sensor and, more particularly, to an acceleration sensor that measures acceleration based on a change in the direction of magnetic field. Furthermore, the present invention relates to an electronic device comprising the same and to an acceleration measuring method as well.
2. Description of the Related Art
For detecting action of a prescribed object, there has been conventionally investigated the use of an acceleration sensor for detecting the acceleration of such object. For example, various applications are considered possible including operation sections of industrial robots, air-bag devices of automobiles, and hard disk drives to be loaded on portable computers, etc. Specifically, for the hard disk drive, it can be used to suppress damages to data through retracting a magnetic head by instantly detecting forcible movement and fall. Furthermore, the acceleration sensor is required for detecting impact imposed on the device and inclination (angle) of the device in addition to the free fall.
As the constitution of an acceleration sensor of a conventional case, a popular method is to detect distortions generated in a structure due to acceleration as disclosed in Patent Literature 1, Japanese Registered Patent Publication No. 2732287, for example. Specifically, a weight is placed at the center (intersection point) of a cross-shaped supporting member that has a spring characteristic, and a distortion sensor element is fixed at each beam section of the supporting member. Then, deformations of each beam are detected based on the detected values of the distortion sensor elements, and there are detected the accelerations in the direction of each of the axes (X, Y, Z). For detecting the acceleration, for example, there is a method where a semiconductor piezoelectric element is used as the distortion sensor element and a bridge circuit is provided for detecting the resistance value thereof, and a method where a piezoelectric vibrator is used for detecting the transmission cycle by the distortion.
However, in the methods of the above-described conventional case, it is necessary to provide electrodes on the cross-shaped supporting member (spring) itself or the vicinity thereof to be used for capturing signals for detecting the distortion. Thus, the structure may be complicated by the wirings. Further, the distortion sensor elements are mounted to the supporting member so that the size thereof cannot be reduced. Furthermore, it has been an issue that displacement of the spring is obstructed so that it becomes difficult to detect acceleration with high precision since the distortion sensor element is mounted or built in the spring part of the supporting member internally.